1. Field of the Invention
This invention relates generally to semiconductor fabrication, and, more particularly, to scheduling work in a fabrication facility.
2. Description of the Related Art
A variety of processing tools are used to fabricate a semiconductor device. The processing tools may include photolithography steppers, etch tools, deposition tools, polishing tools, rapid thermal processing tools, ion implantation tools, and the like. Wafers (or wafer lots) are processed in the tools in a predetermined order and each processing tool modifies the wafers according to a particular operating recipe. For example, a photolithography stepper may be used to form a patterned layer of photoresist (i.e. a mask) above a dielectric layer that has been deposited above the wafer. Features in the patterned layer of photoresist correspond to a plurality of features, e.g. gate electrode structures, which will ultimately be formed above the surface of the wafer. The wafer is then provided to an etch tool that etches away portions of the dielectric layer corresponding to features in the mask to form the plurality of features above the surface of the wafer.
Shop floor work-in-process (WIP) management tools may be used to coordinate operations of the processing tools. Conventional shop floor work-in-process management tools usually include tools for scheduling processing of wafers by the various processing tools. For example, a shop floor work-in-process management tool may include a dispatching tool that determines which wafers should be provided to which processing tools. The dispatching tool typically makes dispatching decisions based on the current state of the processing tools and/or the wafers that are to be processed. However, conventional dispatching tools do not provide information regarding upcoming work that may be performed on wafers by the processing tools. Consequently, conventional dispatching tools do not provide information that may allow the shop floor work-in-process management tools to prepare for future work.
Conventional shop floor work-in-process management tools may also include tools for reporting information related to the processing of the wafers and reviewing the performance of the processing tools. For example, the shop floor work-in-process management tool may include tools for measuring and reporting one or more factory performance metrics associated with processing of the wafers. However, the factory performance metrics are typically determined independent of other operations carried out by other portions of the shop floor work-in-process management tool, such as the dispatching decisions made by the dispatching tool. Thus, the shop floor work-in-process management tool is not generally able to compare the performance of the processing tools to the requests made by other parts of the shop floor work-in-process management tools. For example, the performance metrics generally do not measure compliance with the dispatching decisions made by the dispatching tool.
Plant managers and/or engineers on the shop floor may override the shop floor work-in-process management tool. For example, an experienced engineer may be able to anticipate a problem with one of the processing tools, and may, therefore, override a dispatching tool's request to process wafers in the problematic processing tool. However, even the most experienced engineer and/or plant manager may not be able to anticipate the consequences of overriding a request on the operation of the entire shop floor and/or the performance metrics used to assess the performance of the fabrication facility. Accordingly, even though manual overrides may improve the performance of portions of the fabrication facility, they may degrade the overall performance of the fabrication facility, at least in part because the conventional shop floor work-in-process management tools may not be able to compensate for system-wide effects of the manual overrides.